Air conditioning

by G.F., economist.com
July 17th 2012 8:49 PM

AS AMERICANS endure yet another heatwave, their sole consolation is that it might have been worse were it not for Willis Carrier. Precisely 110 years ago in Brooklyn, on July 17th 1902, in the middle of a warm and wet summer, Carrier signed off on the final drawings of what within a few weeks became the world's first modern air-conditioning unit. It was not designed to waft a merciful chill to the perspiring masses. Rather, the bulky device was intended to regulate humidity at a printing plant. Improving workers' comfort was a side-effect. It was not until the 1930s that air conditioners became widespread in offices and apartment buildings; it took another two decades before they were common in detached homes. The latest developments in the technology are also gracing industrial spaces to start with.

The first active cooling systems date back to the 1840s, and relied on air blown over stored ice or pipes containing pressurised liquid that absorbed heat. Their aim was indeed to cool interiors (sometimes to freezing for food storage). In printing, however, moisture is key. Paper shrinks, expands and warps in response to changes in humidity. Keeping the amount of moisture constant was crucial, especially in full-colour printing, which requires four passes of the same sheet (one for each of the component colours—cyan, yellow and magenta—and another for black). One firm, Sackett & Wilhelms of Brooklyn, was so tired of having to bin stacks of poorly matched magazine pages that it hired Buffalo Forge Company to fix the problem. Buffalo put the young Carrier, considered something of a whiz kid, on the task.

Carrier figured out that moisture could be extracted from the air by having a system of coiled pipes. Half of the coils were kept inside the building, under low pressure. The other half remained outside the walls. The difference in pressure in the closed loop was maintained using a compressor and joints between the system's parts. The warmer air surrounding the indoor coils heated the refrigerant, picked to boil at a low temperature, converting it from a liquid to a gas. The laws of physics dictate "phase changes" like this absorb heat, cooling the pipes. The moisture in the air surrounding the pipes would condense onto the coils and drip into a drain. The now-gaseous refrigerant passed through a compressor that increased pressure and heated the gas further. It further passed into a condenser, over which a fan blew cooler outdoor air. That helps complete a phase change back to a reliquified refrigerant. Heat is conserved, but redistributed from the building's interior to the exterior. Finally, the gas passed through an expansion joint which lowered its pressure—and thus temperature—allowing the process to begin anew. (Refrigerators work the same way, and heat pumps provide warmth thanks to a reverse process.)

A drug firm and a silk mill swiftly followed Sackett & Wilhelms in adopting Carrier's device. A host of other companies in different industries, including Gillette's safety-razor factory where humidity caused corrosion, converted soon after. In 1915 the Carrier Corporation was founded. It exists to this day as a division of United Technologies, an industrial conglomerate.

The basics of air conditioning have not changed much since those early years. Units are smaller and more efficient, thanks to better compressors. Some new ideas, like using waste heat to power phase changes, have yet to catch on. Others are in commercial production, such as building ice on cool nights when power usage is low, and using it to cool the refrigerant. An even older method, called swamp cooling, has made a comeback. It involves misting ambient air to remove heat through evaporation alone. Some data centres, like Facebook's high-desert server farm in Prineville, Oregon, have adopted this approach, which requires a dry climate to work well.

The biggest change is the refrigerant used. Carbon dioxide was one popular choice until the 1920s, when it was abandoned because the high pressure needed to compress it back into a liquid meant having to install robust, and expensive, plumbing. Fluids which replaced it, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), needed less sturdy installations since they boil at low pressure. Their properties also made them ideal refrigerants. But they fell out of favour in the 1970s, when it transpired that they deplete the Earth's ozone layer. The ozone-friendly hydrofluorocarbons (HFCs) which came later turned out to be planet-heating greenhouse gases, up to 15,000 times more potent than carbon dioxide.

Plenty of homes still rely on HFC-based units for now. But that will begin to change as the devices reach the end of their useful life and regulators insist on switching over to greener alternatives. But Carrier's invention will probably not change out of all recognition as it celebrates anniversaries to come.

Original Page: http://www.economist.com/blogs/babbage/2012/07/air-conditioning

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Victor Cuvo, Attorney at Law

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